How to grind in Enslaved? (Spoilers)

I'm playing Enslaved on hard, and am having some trouble with the last portion of Chapter 8 after the you construct the windmill properly and the wave of mechs come endlessly. Someone informed me of getting the Focused Attack to helpand I need a TON of orb points for that. I've tried grinding in Chapter 3, and then exiting before finishing the level but when I go back to the level again to grind more, my orb points go back to the same amount before grinding.

To grind in Enslaved, do I have to complete a full level to allow the orbs to keep on building?

i think so, but i cant remember i didnt really like the game that much to even remember anything about it